The WRC was trying to 'clean up' the cars to make them more recognizable. That meant smaller more compact event placards on the doors, uniform font/color/size of the number and the singular driver name. No doubt this was used to boost TV viewership in lessening confusion.

And yes, Ford and Subaru were bearing both names in Monte Carlo in 2004. They changed the names to Solberg only for the second day of competition. Subaru simply was unaware of the situation and the change in the rules!